In-situ landfill pyrolysis, remediation and vitrification

ABSTRACT

The process or the present invention serves to remediate and reduce the volume of waste materials in a landfill site and increases the useful life of the treated landfill. The process steps involve drilling a series of holes into the waste material mass at proper spacing, inserting and operating a plasma arc torch in each drilled hole to pyrolize, remediate and vitrify the waste materials and allowing the melted materials to cool and harden. During the process, a gaseous by-product is produced and collected in a hood which is attached to scrubbing and chemical cleaning apparatus. The resultant gases are commercially useful as fuel gas and the vitrified residue is significantly smaller in volume than the original waste material volume, thus substantially extending the useful life of the landfill site and ultimately providing a firm foundation for construction.

REFERENCE TO RELATED APPLICATION

Related copending application Ser. No. 07/827,384 filed Jan. 29, 1992for "IN-SITU SOIL STABILIZATION METHOD AND APPARATUS" provides usefulbackground for the present application.

FIELD OF INVENTION

The invention relates to the treatment of residential and industrialwaste as found in a landfill site.

BACKGROUND OF THE INVENTION

Environmental consequences of the contemporary lifestyle in this countryfrequently result in dramatic problems in a number of areas of publicconcern. A major related concern is the need to increase the capacityfor disposing of residential and industrial wastes.

One of the political topics which tends to generate the most publicresponse is the topic of finding a location for a new landfill facility.Everyone generates waste, and yet no one wants to have a waste disposalsite or a waste incinerator nearby. The reasons for this range publicdislike of waste disposal facilities . .ranges.!. .Iadd.range.Iaddend.from toxic hazards, to leaching of dangerous chemicals into thegroundwater, to unpleasant odors and to reduction in real estate values.

Despite this generally held dislike for landfills, the need for morewaste disposal capacity keeps growing. We produce more waste each yearand the existing landfills are rapidly approaching the point of beingfiled to capacity. The problem encompasses residential waste such asbio-degradable and non-biodegradable garbage and industrial wasteincluding scrap, chemical residues, sludge, mill tailings, and otherforms of waste, some of which may be industrial, hazardous, toxic orradioactive. Common municipal solid waste is being generated at the rateof over 200 million tons per year. Over ninety percent (90%) of thiswaste is deposited in landfills. At this rate, more than half theoperating landfills in the country will reach their limit of capacitywithin the next few years. Efforts at recycling, while helpful, fall farshort of coping with the problem.

A typical landfill contains a great variety of materials, only a smallnumber of which will decompose naturally. A weight analysis of landfillcomponents by category indicates paper products (41%), glass and metal(16.9%), plastics (6.5%), rubber and textiles (4.3%), yard waste(17.9%), wood (3.7%) and food (7.9%).

The process of incineration deals somewhat with the capacity problem,but it simultaneously creates other problems, such as pollution, odors,acid rain, depletion of fuels, etc. Incineration, by its nature, is acombustion process and, therefore, generates a number of gaseousproducts which range from unpleasant to dangerous.

Pyrolysis is a chemical decomposition of materials due to the action ofheat. Pyrolysis is distinct from combustion in that oxygen is notpresent and, therefore, the resulting chemical products are different.When pyrolysis or materials is accomplished under sufficiently hotconditions, some gases (potentially useful as fuel) are generated due todecomposition of the organic compounds, and the residue from the wastematerials is melted and solidified (vitrified), thus greatly reducingits volume. The chemical composition of the gases generated by pyrolysiscan be controlled by the introduction of specific additives, such assteam.

The present invention recognizes that there exists a relatively newtechnology which may be employed in the pyrolysis and vitrification ofwaste materials by the application of quantities or very hightemperature heat energy. The basic tool used in this technology is theplasma arc torch. Plasma arc torches can routinely operate attemperatures of 4000° C. to 7000° C. in the range of 85-93% electric toheat energy efficiency. The highest temperature attainable by fuelcombustion sources is in the vicinity of 2700° C.

A plasma arc torch operates by causing a high energy electric arc toform across a stream of plasma, or ionized gas, thus generating largeamounts of heat energy. There are many types of plasma torches. ., butall torches.!..Iadd.. A plasma torch can operate on AC or DC power, useinert, reducing or oxidizing gas, and have metal or graphite electrodeswhich may be solid or hollow. All plasma torches .Iaddend.generally fallinto one of two basic categories according to the arc configurationrelative to the torch electrodes, i.e., transferred arc type andnon-transferred arc type. The arc of a transferred arc torch is formedby and jumps from a single electrode on the torch, through the plasmagas, and to an external electrode which is connected to an oppositeelectrical pole. The arc of a non-transferred arc torch is formed by andjumps from one electrode on the torch across the plasma gas to anotherelectrode on the torch.

In a plasma arc torch, the heat energy produced is proportional to thelength of the arc, assuming the type of plasma gas and flow ofelectrical current both remain constant.

Since the present invention makes use of a plasma arc torch, referenceis next made to U.S. Pat. No. 4,067,390 granted to the present inventorsfor "Apparatus And Method For The Recovery Of Fuel Products FromSubterranean Deposits Of Carbonaceous Matter Using A Plasma Arc" whichteaches the use of a plasma arc torch to gasify or to liquifyunderground deposits of coal, oil, oil shale and other carbonaceousmaterials. The teachings of the '390 patent are incorporated herein byreference.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for reducing thevolume of waste products, including those containing toxic or low-levelradioactive materials, in a safe manner and for generating andcollecting potentially useful gases at the same time. A plasma torch isinserted to the bottom of a drilled and cased hole in a landfill that isclosed or approaching its capacity. The torch is energized in thenon-transferred mode to generate heat in the 4,000°-7,000° C. range soas to pyrolyze and vitrify materials in its vicinity. Useful gases forcogenerataion or as an alternate fuel source are simultaneouslygenerated, collected and cleaned; i.e., the effluent gases must betreated to ensure that no hazardous effluents are released to theatmosphere. Due to the natural low density of landfill wastes, thevitrified waste materials are considerably more compact than theoriginal materials. As the waste becomes more melted, a molten poolforms, a void is created around the torch and additional waste fallsinto the molten pool, adding to the melt. As the level of the moltenpool rises and approaches the plasma torch, the torch is raised in theborehole to a new operating level. This process is repeated insuccessive holes throughout the landfill until the entire landfill hasbeen treated and the surface level of waste has subsided to near thebottom of the landfill basin. When the reduction of the waste volume hasseen completed, the process of filling with added municipal orindustrial waste is resumed. The entire procedure of pyrolysis andvitrification is repeated a number of times over a number of years untilthe level of vitrified material residue builds up to where it is at ornear the original ground level. Thus, the landfill is fully remediated,the useful life of the landfill has been extended and a firm, inertfoundation for construction has been established.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation presented as a series of steps A-Hof a landfill site portraying the method of the invention beingpracticed sequentially over time to minimize the volume of waste whilemaximizing landfill life and land utilization.

FIG. 2 is a sectional elevational view of the method and apparatus ofthe invention illustrating a plasma torch installed in a drilled holeextending to the bottom of a landfill and a gas collecting hoodassembled above the processing hole.

FIG. 3 is a flow chart representation of the process of the inventionindicating the input and output products.

FIG. 4 is a plan view of the surface of a landfill site after treatmentaccording to the invention, showing the original borehole locations indashed lines.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Depicted in a series of process steps in section view in FIG. 1, basin10 is a natural or manmade cavity in the surface of the earth whichserves as the site of a typical landfill into which materials are dumpeduntil no more space is available. At that time, the waste material.canbe completely remediated and a volume reduction according to the presentinvention may be employed to increase the life and effective capacity ofthe site. In FIG. 1, step A, the landfill basin 10 is filled with wastematerials 12 to approximately its capacity. According to the method andby utilizing the apparatus of the invention, as will be described indetail later, waste remediation and a significant reduction in thevolume of the former waste material 12 may be accomplished.

The result of the first phase of remediation and reduction in wastevolume is illustrated in FIG. 1, step B, wherein the basin 10 stillcontains untreated waste materials 12 and treated, or vitrified residue14. As it is shown, the pyrolysis and vitrification process to bedescribed effectively reduces the volume of material in comparison tothe untreated waste material 12.

The treatment process is continued in successive locations throughoutthe landfill area until a condition approximating that portrayed in FIG.1C is reached in which all the waste materials which had previouslyfilled basin 10 are now remediated and reduced by pyrolysis andvitrification to a fraction of their original size in the form of ahard, glass-like, vitrified residue 14. Optionally, multiple locationsof waste within a landfill site may be treated simultaneously so as toreduce the time required for the total process. Thereafter, for a periodof time, additional waste material 12 may be deposited into basin 10 ontop of vitrified residue 14 until the level of waste materials 12 againreaches the maximum volume capacity as shown in FIG. 1D.

A process approximating that described above in regard to steps 1B and1C is undertaken again to result in a volume of vitrified residue 14 asillustrated in FIG. 1E. The resultant volume of vitrified residue 14 asrepresented in FIG. 1E is the total amount from the first and secondvitrification processes shown in FIGS. 1C and 1E.

Subsequently, additional waste material 12 is dumped into the basin 10to arrive at the condition shown in FIG. 1F, which, after several cyclesof this process, will be followed by a further pyrolysis andvitrification process resulting in a vitrified residue 14 which, afterseveral cycles of the inventive process, ultimately approximates themaximum capacity of basin 10 as shown in FIG. 1G. The actual number ofsteps required to complete this sequential vitrification process andresult in a vitrified residue 14 which is substantially level with thetop of basin 10 will vary according to a number of factors such as thewaste composition and depth. FIG. 1 is therefore a somewhat simplifiedsequence for purposes of illustration.

When the vitrified residue 14 is at or near the level of the earthsurrounding basin 10, and due to the extremely hard, dense and inertnature of vitrified residue 14, it is possible and useful to constructupon vitrified residue 14, returning the land to a further usefulpurpose, as illustrated in FIG. 1H. The exposure of waste materials 12to the extremely high temperatures of the invention process (discussedbelow), in addition to reducing volume of waste, effectivelyneutralizes, gasifies, or immobilizes the original contaminants and lowlevel radioactive materials, thus making a safe and strong base forfuture construction. Whereas the typical filled landfill site is totallyunsuited and hazardous as a building site because of subterranean toxicmaterials, settlement and potentially explosive gases, the method of theinvention, by contrast, provides the mentioned strong and safefoundation for future construction.

In addition to providing a societal useful purpose for the landfill siteafter it has filled all available space, the invention has, as describedabove, effectively remediated the waste materials, increased the usefullife and effective capacity of the landfill site to a substantialextent, and reclaimed commercially useful gases.

To accomplish the objectives of the invention as portrayed in theforegoing description of the method employed, a source of high heatenergy is needed. A particularly controllable and efficient source ofhigh temperature heat is the plasma arc torch. A typical plasma arctorch which is suitable for treating waste materials has a one megawattelectrical power rating and is of cylindrical shape, approximately 22 cmin diameter. It is preferred, in reference to FIG. 2, that the diameterof the formed hole be 5-10 cm larger than the diameter of the plasmatorch. Therefore, as illustrated in FIG. 2, borehole 30 is formed, e.g.by drilling, to have about a 30 cm diameter for torch clearance. Plasmatorches of higher power ratings are generally proportionally larger indiameter. Torches rated at from 300 kw to 10 Mw power rating can beemployed according to the requirements of the landfill, provided thehole diameter is appropriate and adequate electrical power is available.A plasma torch applicable to the method and apparatus of the inventionis produced by Plasma Energy Corporation, Raleigh, N.C. It is generallydesirable to insert a substantially rigid tubular casing made of anyheat destructible material, such as thin metal, into the drilledborehole 30. The casing acts to prevent sidewall collapse and tofacilitate the movement of plasma torch 16 down and up borehole 30. Soas to additionally facilitate insertion and movement of plasma torch 16,hole 30 is drilled vertically into the landfill waste mass 12.

Plasma torch 16, preferably with arc forming means operative to form anon-transferred arc, is lowered into cased borehole 30 with plasma gas,electric supply and cooling water lines connected, which utility linesare carried by a common supply conduit 18. A protective heat resistantshroud 20 is provided and extends upwardly from the upper portion ofplasma torch 16 to insulate the utility lines carried in supply conduit18 from the damaging heat travelling convectively upward in hole 30.Plasma torch 16 is energized to generate heat in the range of 4000° C.to 7000° C., which is hot enough to readily melt the borehole casing anddecompose and pyrolyze the waste materials 12 surrounding hole 30. Torch16 transmits its heat energy by a combination of radiation andconvection. The majority of the convection heat will travel upward alongbore hole 30, and the radiation energy will begin to melt the wastematerials 12 around bore hole 30 and will create a substantiallyspherical chamber 25 as the waste melts and collects in a pool of moltenwaste 24.

Beyond the ability of a plasma arc to operate at exceedingly hightemperatures, the energy generated is unusual in its frequencydistribution. The energy generated by conventional combustion processesoccurs mostly in the infrared section of the electromagnetic spectrum,largely in the visible light section and marginally in the ultra-violetsection. By contrast, the energy generated by a plasma arc will be asmuch as 29% in the ultra-violet portion of the spectrum. Ultra-violetenergy wavelengths are able to penetrate gasses without measurable heatloss and to penetrate solids more quickly and effectively than infra-redwavelengths.

The operating plasma torch 16 utilizes an ionized gas flowing underpressure and forms an electric arc supported by that gas. Input electricpower, plasma gas and coolant are each regulated by conventional means(not shown) located within a suitable control panel 34.

As the heat of plasma arc flame 22 pyrolyzes waste materials 12,spherical chamber 25 develops and widens around torch 16. As the levelof the molten pool rises and approaches the plasma torch, the torch 16is raised in the borehole to a new operating level 25, thus providingadditional material for plasma torch 16 to pyrolyze into molten wastematerial 24. Plasma torch 16 may be raised automatically or by manualcontrols. This process may encompass a volume of up to five (5) metersin diameter, according to the characteristics of the waste 12 and thepower level of plasma torch 16.

When a column of the diameter of chamber 25 and a height up to the topof basin 10 is pyrolyzed and the vitrified residue 14 sits at itsbottom, plasma torch 16 is deenergized and removed. A torch liftingmechanism 26 and pulley 28 are employed to remove plasma torch 16. A newborehole is formed in another position in the landfill and the processis repeated until the entire volume of the landfill has been treated.The spacing of additional boreholes 30 for treating additional wastematerial 12 in the landfill will be determined according to theeffective diameter of the column achieved at first borehole 30 so as totreat the entire landfill volume and ensure that successive vitrifiedcolumns coalesce into a solid mass.

FIG. 4 illustrates a typical arrangement of boreholes 30 in a landfillbasin 10. Boreholes 30, shown in dashed lines, are separated by adistance such that when the vitrified residue 14 has cooled, theindividual vitrified columns will have coalesced together to asubstantially solid, continuous mass on which future construction may bebuilt.

During the described process of melting waste materials 12, the heatingoccurs in an area accessed by a relatively small diameter borehole 30.In this situation, little if any atmospheric air reaches the site of thehigh heat application. The plasma gas used may be air, since it iseconomical and readily available, but the quantity of air supplied tosupport the plasma arc flame 22 is so much less than the amount neededto burn the quantity of waste being treated as to be negligible. Underconditions of high heat and little air, or oxygen, combustion is notpossible. At the same time, pyrolytic chemical reactions, includingdecomposition of some of the waste materials and further reaction withadded steam (see FIG. 3) will take place. These chemical reactions giveoff a variety of gases, some of which are commercially useful,particularly as fuel. These resultant gases include hydrogen, carbonmonoxide, carbon dioxide, methane, nitrogen and others. An analysis oftypical gases resulting from the process described indicates a total of27,000 standard cubic feet of gas by-product generated from each ton oftypical municipal waste materials pyrolyzed. Processing of industrial orother special waste materials may result in a different volume anddifferent types of gases given off.

A gas collecting hood 32, as shown in FIG. 2, is placed over the top ofborehole 30 to trap and route the gases produced to a treatment station,such as a cleaning operation, prior to storage for recycling. Gases exitgas collecting hood 32 at arrow 36, representing output gases, and areconducted into a piping system (not shown) for chemical cleaning orscrubbing.

The pyrolysis, remedation and vitrification of waste materials by theplasma torch and the subsequent handling of the gas by-product isdepicted in the form of a process chart in FIG. 3. Plasma torch 16 issupplied with its three needed inputs, i.e. plasma gas, electric energyand cooling water. The water is not fed as a utility supply to the torch16, but circulates around and within the body of torch 16 so as toprevent the plasma torch 16 from being destroyed by its own heat. Theoutput from torch 16 is heat energy which is applied to operate on wastematerials 12. In order to generate the desired gaseous by-products asdescribed above, it may be necessary to introduce a quantity of water tothe materials 12 being treated, in the form of steam which isapproximately equal in weight to the quantity of waste material 12 beingprocessed.

The resultant output of the process described comprises vitrifiedresidue 14, gas by-product 36 and water. The water output from the wastetreatment process is recycled back into the water supply to make steam.A vitrified residue 14 remains in a column near the bottom of hole 30(FIG. 2), which column will eventually be coalesced with other vitrifiedcolumns produced in the landfill. This layer will be the final formafter the remediated, molten waste 24 has cooled and solidified. The gasby-product 36 is next transmitted through a cleaning chemical 38 whichboth filters the gaseous effluent and reacts with it chemically toimprove the value of and commercial usefulness of the result.

Plasma arc torches as are used in the present invention also aresubstantially unaffected by the presence of water in the operatingenvironment. These torches, particularly as operated in thenon-transferred mode, will operate under water, thus being effectiveeven if the landfill basin is partially filled with water, liquid wastesor the like.

By the process described above, the volume occupied by waste materialsin a landfill is reduced to a small percentage of its original volume ineach successive remediation and volume reduction procedure, depending onthe nature of the materials treated.

Whereas the description above related to landfill sites primarily usedfor residential municipal waste, the principles are applicable as wellto deposits of industrial wastes, including hazardous or toxic wastes,whether enclosed in scaled containers or in loose form. Situations suchas dumps for drums of undesirable petroleum by-products, highly activecleaning agents, low level radioactive materials or heavy metals areequally susceptible to the treatment herein described. Due to theefficiency and high energy output of the plasma arc torch, the organicmaterials are broken down by pyrolysis essentially into harmless basicelements and compounds to recombine into useful gases, and the inorganicremainders are vitrified and significantly reduced in volume. The natureof the vitrification is such as to effectively immobilize, encapsulateand make unleachable any residual dangerous materials. The particularsof which plasma gas to use, what degree of heat is appropriate, andwhether to process the output gas by-product through a cleaning step forcommercialization, as with the case of municipal landfill, depends uponthe exact nature of the waste materials involved. The scope andprinciples of the invention disclosed are not to be considered limitedby the particulars of the preferred embodiment described herein, but aredefined by the claims which follow.

We claim:
 1. A method for in-situ treatment and remediation of wastematerials collected in a landfill by means of a plasma torch havingappropriate connected utilities, comprising .Iadd.the stepsof.Iaddend.:(a) forming a borehole of a size sufficient to accommodate aplasma torch and extending from an upper end to a lower end at apredetermined depth below the landfill's top surface and passing throughwaste materials collected in the landfill; .Iadd.(b) inserting a casinginto said formed borehole for preventing sidewall collapse; .Iaddend. ..(b).!. .Iadd.(c) .Iaddend.lowering a plasma torch with connectedutilities into said formed borehole and suspending the torch at alocation above and proximate said borehole lower end; . .(c).!..Iadd.(d) .Iaddend.utilizing the connected plasma torch utilities tooperate said torch .Iadd.to convert electrical energy to heat so as.Iaddend.to create a plasma arc flame of sufficient temperature topyrolize, remediate and vitrify. ., substantially in the absence ofcombustion,.!. said waste materials located proximate said plasma arcflame, thus forming a molten mass, and permitting any resultantby-product gases to rise in said formed borehole; . .(d).!. .Iadd.(e).Iaddend.collecting said by-product gases for treatment and recycling; ..(e).!. .Iadd.(f) .Iaddend.deenergizing the torch and stoppingproduction of said plasma arc flame; . .(f).!. .Iadd.(g) .Iaddend...removing.!. .Iadd.raising .Iaddend.the plasma torch with its connectedutilities from the borehole; and . .(g).!. .Iadd.(h) .Iaddend.allowingsaid molten mass to cool and solidify thereby to produce a . .column.!..Iadd.mass .Iaddend.of remediated and vitrified waste material ..which.!. .Iadd.whose .Iaddend.volume is substantially less than thevolume of waste material from which the vitrified . .column.!..Iadd.material .Iaddend.was produced.
 2. A method for in-situ pyrolysis,remediation and vitrification of waste materials collected in a landfillas claimed in claim 1 further comprising the step of . .inserting a.!..Iadd.forming said casing of a .Iaddend.heat destructible . .casing intosaid formed borehole prior to lowering said torch therein.!..Iadd.material.Iaddend..
 3. A method for in-situ pyrolysis, remediationand vitrification of waste materials collected in a landfill as claimedin claim 1 in which said formed borehole is substantially vertical.
 4. Amethod for in-situ pyrolysis, remediation and vitrification of wastematerials collected in a landfill as claimed in claim 3 in which thestep of collecting a gas by-product is accomplished in a gas collectinghood covering the top of said formed borehold.
 5. A method for in-situpyrolysis, remediation and vitrification of waste materials collected ina landfill as claimed in claim 1 further comprising the step ofvitrifying waste material by repeating the method claimed in a pluralityof boreholes formed in the landfill.
 6. A method for in-situ pyrolysis,remediation and vitrification of waste materials collected in a landfillas claimed in claim 1 further comprising the step of selecting thedistance between adjacent holes so that respective melted and solidifiedcolumns coalesce together.
 7. A method for in-situ pyrolysis,remediation and vitrification of waste materials collected in a landfillas claimed in claim 1 further comprising the step of operating saidplasma torch in a non-transferred mode.
 8. A method for in-situpyrolysis, remediation and vitrification of waste materials collected ina landfill as claimed in claim 1 further comprising the step .Iadd.priorto removing the plasma torch with its connected utilities from theborehole .Iaddend.of raising said plasma torch in said borehole tooperate at a new level. . .9. A method for in-situ pyrolysis,remediation and vitrification of waste materials collected in a landfillas claimed in claim 2 in which said formed borehole is substantiallyvertical..!.10. A method for in-situ pyrolysis, remediation andvitrification of waste materials collected in a landfill as claimed inclaim 4 further comprising the step of vitrifying waste material byrepeating the method claimed in a plurality of boreholes formed in thelandfill.
 11. A method for in-situ pyrolysis, remediation andvitrification of waste materials collected in a landfill as claimed inclaim 5 further comprising the step of selecting the distance betweenadjacent holes so that respective melted and solidified columns coalescetogether.
 12. A method for in-situ pyrolysis, remediation andvitrification of waste materials collected in a landfill as claimed inclaim 6 further comprising the step of operating said plasma torch in anon-transferred mode.
 13. A method for in-situ pyrolysis, remediationand vitrification of waste materials collected in a landfill as claimedin claim 7 further comprising the step .Iadd.prior to removing theplasma torch with its connected utilities from the borehole .Iaddend.ofraising said plasma torch in said borehole to operate at a new level.